Cluster TOF‐SIMS imaging of human skin remains: analysis of a South‐Andean mummy sample

Abstract

A skin sample from a South-Andean mummy dating back from the XI(th) century was analyzed using time-of-flight secondary ion mass spectrometry imaging using cluster primary ion beams (cluster-TOF-SIMS). For the first time on a mummy, skin dermis and epidermis could be chemically differentiated using mass spectrometry imaging. Differences in amino-acid composition between keratin and collagen, the two major proteins of skin tissue, could indeed be exploited. A surprising lipid composition of hypodermis was also revealed and seems to result from fatty acids damage by bacteria. Using cluster-TOF-SIMS imaging skills, traces of bio-mineralization could be identified at the micrometer scale, especially formation of calcium phosphate at the skin surface. Mineral deposits at the surface were characterized using both scanning electron microscopy (SEM) in combination with energy-dispersive X-ray spectroscopy and mass spectrometry imaging. The stratigraphy of such a sample was revealed for the first time using this technique. More precise molecular maps were also recorded at higher spatial resolution, below 1 µm. This was achieved using a non-bunched mode of the primary ion source, while keeping intact the mass resolution thanks to a delayed extraction of the secondary ions. Details from biological structure as can be seen on SEM images are observable on chemical maps at this sub-micrometer scale. Thus, this work illustrates the interesting possibilities of chemical imaging by cluster-TOF-SIMS concerning ancient biological tissues.

Improved mass resolution and mass accuracy in TOF-SIMS spectra and images using argon gas cluster ion beams

“…One attempt to improve mass resolution in TOF-SIMS using Ar-GCIB involves applying delayed extraction, an essential technique in TOF mass spectrometry. [17][18][19][20][21][22][23][24][25][26][27][28] In the conventional static extraction mode (standard mode) of TOF-SIMS analysis, the width of the primary ion pulse directly affects the start accuracy of the TOF measurement, regardless of whether the analysis is performed with Ar-GCIB or with a liquid metal ion gun. This is because the pulsed primary ions desorb the secondary ions while the extraction field is already switched on, as shown in Scheme 1(a).…”

Study of skin of an Egyptian mummy using a scanning electron microscope

“…The imprints of ancient bandages revealed during the research made it possible to unambiguously confirm the origin of the forearm from an ancient Egyptian mummy. The suggested method can successfully be applied for both archeological and forensic medicine studies (Cersoy et al 2012, Cotte et al 2004). …”

From Archaeological Sites to Nanoscale: The Quest of Tailored Analytical Strategy and Modelling

“…b Hypodermis area, two color overlay between ion images (protein backbone in red (R) and fatty acids in blue (B). Field of view 200 × 200 mm 2 ; 512 × 512 pixels, pixel size 390 nm (Cersoy et al 2012) clearly that nanoscale techniques can provide unique information about the chemical composition and structure of ancient materials. Unfortunately, almost all of these techniques imply the sampling of heritage artefacts, not always allowed regarding conservation policies.…”

“…ToF-SIMS (Fig. 7) has been used to analyse painting pigments (Richardin et al 2011) or human skin remains (Cersoy et al 2012). Concerning nano-SIMS, this technique is mostly used in the geoscience field (see for example Hoppe et al 2013).…”